Ion implantation is a standard technique for introducing conductivity-altering impurities into substrates. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the substrate. The energetic ions in the beam penetrate into the bulk of the substrate material and are embedded into the crystalline lattice of the substrate material to form a region of desired conductivity.
Solar cells provide pollution-free, equal-access energy using a free natural resource. Due to environmental concerns and rising energy costs, solar cells, which may be composed of silicon substrates, are becoming more globally important. Any reduced cost to the manufacture or production of high-performance solar cells or any efficiency improvement to high-performance solar cells would have a positive impact on the implementation of solar cells worldwide. This will enable the wider availability of this clean energy technology.
Solar cells may require doping to improve efficiency. The dopant may be, for example, arsenic, phosphorus, or boron. FIG. 1 is a cross-sectional view of an interdigitated back contact (IBC) solar cell. In the IBC solar cell, the p-n junction is on the back side of the solar cell. In some embodiments, as shown in FIG. 2, the doping pattern may comprise a plurality of n-type dopant regions 204 distributed throughout a p-type dopant region 203. The p+ emitter 203 and the n+ back surface field 204 are appropriately doped. This doping may enable the junction in the IBC solar cell to function or have increased efficiency.
Typically, the dopant pattern shown in FIG. 2 is made using a hard mask, which is directly formed on the substrate. For example, a mask material may be applied to the entire substrate. The hard mask material then is patterned such that the mask material is removed only in those regions which are to be n-doped. The exposed areas can then be doped, using methods including diffusion, ion implantation, or other appropriate doping method. After the doping process is completed, the hard mask may be removed. If appropriate, this process could be repeated in order to form additional patterned doped regions on the substrate.
Note that the hard mask technique requires a substantial number of process steps (including forming the masking material, patterning the masking material, and removing the mask after the doping process. Therefore the hard mask method is time consuming and costly.
It would be beneficial if the formation of patterned doped regions can be made without direct application of material to the substrate. For example, it would be advantageous if this pattern could be created using only shadow masks.